Cation Vacancy‐Mediated Ultrafast Hole Transport in CuBi2O4 Photocathodes

In this study, the ultrafast transport dynamics of the valence band hole states in CuBi2O4 (CBO) photocathodes were investigated by varying the atomic composition and manipulating their p‐type character. As a comprehensive ultrafast optical transient absorption spectroscopy (TAS) investigation of compositionally manipulated CBO that combines both ex situ and in situ TAS experiments with photoelectrochemical (PEC) performance tests, the study reveals the polaron formation tendencies of the valence band (VB) holes at cationic vacancy sites. Therefore, it draws a complete picture of the ultrafast hole transport dynamics and provides valuable insights into the hindrance of the photocurrent generated in CBO.